It does what it should, that is, in the rain, as a water repellent, it improves your visibility, the wiper moves more smoothly and less (so it wears out less as well).
For it to have the good and expected results, proper application is necessary, which means: in environmental conditions without high humidity, good washing and cleaning of the windshield and windows. Then apply RainX with a microfiber cloth – you don’t need much, but the cloth should be damp. Apply with S-shaped motions, then vertical and then horizontal – so it gets into all the pores of the glass. Let it dry for about 5 minutes and it usually leaves a slightly faint white due to its active ingredients (this faint white is what some other users mention as a disadvantage, saying it worsens visibility at night). Then with another microfiber cloth, completely dry, wipe it well and this faint white disappears and it becomes "crystal clear." Ready.
If it doesn’t rain immediately after you apply it, pour some water from a bottle on it to see how it slides off.

With one RainX package, I estimate it lasts about two years.
However, I deduct one star because it is EXPENSIVE.